The present invention relates to a method used in paper making for treatment of a weave. More particularly, the invention relates to a method used in paper making for treatment of a weave such as, for example, felt, or paper or board web being produced, and relates especially to a method for improving the maintenance of felt or the removal of water from paper or board web, or for carrying through other similar objectives.
In the method of the invention, ultrasonic sensors/radiators (hereinafter, radiators) or similar audio frequency radiators, or series of radiators arranged in the vicinity of the material to be treated, are used. Coupling liquid is provided between the material being treated and the sensors. The coupling liquid is either special coupling liquid, preferably water, brought to the area of operation, or water eliminated from the paper or board web.
A well known method associated with paper making is the use of high frequency vibrations such as, for example, longitudinal vibrations, of ultrasonic frequency. With regard to this method, reference is made, by way of example, to the following patent literature: CH-PS No. 395,723, DE-PS Nos. 884,457; 943,029; 1,185,469 and 1,957,469, French Pat. No. 1,423 and U.S. Pat. Nos. 3,688,527; 3,829,328 and 4,191,611.
The state of the art is disclosed in an article in the Paper Trade Journal, Jan. 15, 1977, pp. 23-26.
Reference is also made to Finnish patent application No. 802180 of the present inventor; it being the objective of the present invention to further develop the method presented therein.
The state of the art more specifically related to the present invention is described in the aforementioned three patents and the article. In the state of the art described in these publications, a cleaning head, fitted with an ultrasonic vibration amplifier that functions as a radiator of longitudinal vibrations, and installed in the vincinity of the felt, is used to improve the cleaning of the felt of the wet press of a paper machine. A passive acoustic reflector is provided opposite the cleaning head. Devices are arranged before the cleaning head, on the same side. The devices convey on the felt surface liquid, which may act both as cleaning agent and as coupling liquid for ultrasonic vibrations.
In this well known technique, resonance between the cleaning head and the acoustic reflector is used in such a way that the distance between the cleaning head and the acoustic reflector, that is the length of space through which the felt being cleaned, or another weave, passes, is pitched to the length of the half-wave, or 1/2 wavelength, of the acoustic vibration, or to a multiple of said half-wave length, or n.multidot..lambda./2. In this manner, resonance is created in which the phase of the wave reflected from the passive acoustic reflector is the same as the phase of the oncoming wave. This results in the production of such a high intensity ultrasonic field in the material being cleaned, that impurities, such as fibers, are removed from the felt or similar material.
It is now emphasized that the present invention is in no way restricted to ultrasonic frequencies. Acoustic frequencies within the auditory range may also be used in the method of the invention, provided their frequency such as, for example, several kHz, is sufficient to produce the intended effects.
In the aforementioned Finnish patent application No. 802180, the use of ultrasonic waves and longitudinal acoustic vibrations of relatively high frequency within the auditory range is presented in several different functions in the paper making process. Said patent application discloses that, in the paper making process, ultrasonic waves or vibrations of relatively high frequency within the auditory range are used in the water elimination equipment of a paper machine, in a pulp refiner, in a mixing pump for paper making pulp, in the suction box of a paper machine, and/or in the press section roll, or the like. This is accomplished by focusing, by means of parts of the aforementioned equipment, an intensive high frequency acoustic field on the paper web or on the fibers of the pulp suspension. The water removed from the paper web or pulp suspension serves as coupling liquid that conducts vibrations of acoustic frequency.